STEREOCHEMISTRY OF EPHEDRINE AND #-EPHEDRINE
Jan. 5, 1957
a t 220-240" to rosettes of needles, 245' sintering), [aIMD -31.1 f 0.2 (C 0.8%, H20). Anal. Calcd. for C6HllX08: C, 49.64; H, 7.64; N, 9.65. Found: C, 49.44; H, 7.69; N, 9.46. Synthesis of the Two Diastereoisomers of 5-HydroxyD, L-pipecolic Acid. Diethyl 2-( 3 '-Butenyl)-2-f ormamidomal~nate.~~-Diethylaminomalonate was prepared by hydrogenating diethyl isonitrosomalonate a t 1500 p.s.i. using 10% palladium-charcoal,3a b.p. 93-98' (2.5 mm.), 85.5% and formylated in toluene with 90% formic acid31to yield diethyl foryamidomalonate. b.p. 145-150" (3.25 mm.), m.p. 47-49 , 75% yield. To a solution of one equivalent of sodium ethoxide in 50 ml. of absolute ethanol there was added 17.4 g. of diethyl formamidomalonate. The mixture was heated to gentle boiling under roeflux and then 11.6 g. of 3-butenyl bromide (b.p. 98-102 , yield 74% from 3buten-1-01~~) was added slowly. Using essentially the directions of Weisiger, there was obtained, after one recrystallization of the crude product fr?m ethanol, 10.2 g. (46.2%) Two additional recrysof colorless crystals, m.p. 94-96 tallizations from aqueous ethanol yielded the analytical sample, m.p. 96-97" (reported m.p.18333 84'). Anal. Calcd. for C12H1905N: C, 56.02; H, 7.44; N, 5.46. Found: C,55.98; H,7.59; N,5.46. Diethyl 2-(3',4'-Epoxybutyi)-Z-formamidomalonate (IX). -By the use of perbenzoic rather than peracetic acidIg a simpler procedure and higher yields were made possible. A solution of 5.14 g. (0.02 mole) of diethyl 2-(3'-butenyl)-2formamidomalonate in chloroform was treated with a chloroform solution of 0.022 mole of perbenzoic acid. After 4 days a t 4' titrations indicated that the reaction was 98.3% complete. A t this point 50 ml. of water containing several drops of phenolphthalein was added to the chloroform solution of the reaction products. The mixture was treated dropwise with 5 N sodium hydroxide solution until the aqueous phase was alkaline. The chloroform solution then was washed with water, dried over sodium sulfate and freed of chloroform a t reduced pressure. The residue was 4.8 g. of a pale yellow liquid which crystallized on standing, m.p. 73-78". Recrystallization of the crude product from acetone-ligroin (66-68" ) and benzene-ligroin (66-68") effected little purification so it was subjected to a four-funnel countercurrent distribution using 20 ml. of benzene to 100 ml. of water-methanol (1:1). Concentration of the combined water-methanol phases a t reduced pressure and recrystallization of the residue from benzene-ligroin (66-68") yielded 2.76 g. (50.6%) of epoxide, m.p. 79-84' (reported' 75' ). Three recrystallizations from benzene-ligroin (6668') yielded the analytical sample, m.p. 78.5-83.0".
.
(30) Roche Products Ltd., A. Cohen and J. A. Silk, British Patent 611,600, Nov. 1, 1948; C. A , , 43, 3445 (1949). (31) "Organic Syntheses," Coll. Vol. 111, John Wiley and Sons, Inc., New York, N. Y., 195i5, p. 590. (32) R . P. Linstead a n d H. N. Rydon, J. Chem. Soc., 1955 (1934). (33) Dr. Weisiger kindly supplied us with a sample of the compound which was recrystallized from chloroform; it had m.p. 95-96O.
197
Anal. Calcd. for C ~ ~ H I Q O ~C,N :52.74; H, 7.01; N, 5.13. Found: C,52.53; H,7.18; N,5.19. 5-Hydroxypipecolic Acid (I).-A solution of 0.1 g of diethyl 2-(3',4'-epoxybutyl)-2-formamidomalonate ( I X ) in 10 ml. of N sodium hydroxide solution was allowed to stand
.
a t 37' for 3 days. Ten ml. of concentrated hydrochloric acid then was added to the solution. The mixture was boiled under reflux for 5 hr. and then evaporated to dryness a t reduced pressure. Two 10-ml. portions of ethanol were added to the residue and evaporated. The residue was dissolved in 10 ml. of water and the resulting solution was adjusted to pH 6.5 with ammonia water and filtered from a small amount of an amorphous solid. A two-dimensional paper chromatogram of the solution prepared with 2,4lutidine-t-amyl alcohol and n-butyl alcohol-acetone-ammonia indicated the presence of two pairs of diastereoisomeric secondary amino acids and a primary amino acid. One pair with ninhydrin gave a yellow color which exhibited a brick-red fluorescence in the ultraviolet light; these two secondary amino acids presumably were the cis- and trans5-hydroxymethylprolines ( X I and XII). The other pair gave a violet color with ninhydrin which exhibited a bright red fluorescence in ultraviolet light. Paper chromatographic comparison with natural 5-hydroxypipecolic acid isolated from dates indicated that the amino acids were normal and allo-5-hydroxy-n, L-pipecolic acid (racemes of I and V). The remaining amino acid gave a blue color with ninhydrin, was deaminated with nitrous acid, behaved like serine on paper chromatography and presumably was 5,6-dihydroxy-2-aminocaproicacid. The relative intensities of the colors produced with ninhydrin indicated that the non-cyclic amino acid was much more abundant in the crude product than either of the cyclic amino acids and the 5hydroxypipecolic acids were the least abundant. T h e crude product was analyzed on a 150-cm. column of Dowex50 using 0.15% ninhydrin solution in glacial acetic acid and measuring the absorption a t 350 and a t 375 mp. The results of the analysis are shown in Fig. 1. The two smaller peaks, C and D, are those of normal and allo-5-hydroxyD,L-pipecolic acids, respectively, and the two larger peaks presumably are those of the diastereoisomeric 5-hydroxymethylprolines (XI and X I I ) . I n another attempt a t synthesis a solution of 0.1 g. of diethyl 2-(3',4'-epoxybutyl)-2formamidomalonate (IX) in 5 ml. of a 0.42 N solution of anhydrous hydrogen chloride in ether was allowed to stand a t room temperature for 3 hr. The ether was then evaporated in a stream of nitrogen. Ten ml. of 0.5 -47 barium hydroxide solution was added to the residue and the mixture boiled under reflux for 3 hr. Ten ml. of concd. hydrochloric acid then was added and the mixture boiled under reflux for 3 hr. Silver sulfate was added and the mixture digested on a hot-plate and filtered. The filtrate was adjusted to pH 6 with ammonia water and filtered. h twodimensional paper chromatogram of the solution of products indicated that the same products were present in approximately the same relative amounts as were present in the previous synthesis. BE~HESDA, MARYLAND
[CONTRIBUTIONFROM THE NATIONAL INSTITUTE O F ARTHRITISAND METABOLIC DISEASES,NATIONAL INSTITUTES O F HEALTH]
Studies on the Stereochemistry of Ephedrine and $-Ephedrine* BY BERNHARD WITKOPAND CALVIN M. FOLTZ RECEIVED MAY3, 1956 The epoxides obtained from the quaternary bases of ephedrine, Le., ~c-erythro-l-phenyl-l-hydroxy-2-methylaminopropane, and of +ephedrine, i.e., ~~-threo-l-phenyl-l-hydroxy-2-methylaminopropane, are ~-threo-l-phenyl-l,2-epoxypropane (111) and ~-erythro-l-phenyl-l,2-epoxypropane (IV). The Walden inversion occurring in the epoxide formation at the carbon which loses the trimethylamine group, was proved by catalytic reduction of I11 and IV. Both epoxides yielded the same ~-gZycero-l-phenyl-2-hydroxypropane (V) characterized as the p-toluenesulfonate. Acid-catalyzed hydrolytic ring opening of the epoxides I11 and I V yielded as major products ~-erythro-l-phenyl-1,2-propanediol (VI), characterized as the dibenzoate, m.p. 95.5-97', and D-threo-1,2-propanediolVII, m.p. 62", [ a ]-60', ~ dibenzoate m.p. 89.591'.
The Hofmann degradation of the quaternary salts of ephedrine leads t o optically active oxides of
/3-methylstyrene. Although this reaction was discovered in 1902,'a2 the steps and products of this
Presented in part a t t h e 8th Summer Seminar in the Chemistry of Natural Products, Grand Manan Island, New Brunswick, August
(1) E. R. Miller, Arch. Pharm., 240, 481 (1902); H. Emde, ibrd., 244, 241 (1906): P.Rabe, &I., 43,884,2622(1910); 44,824 (1911). (2) E.Schmidt, Arch. P h ~ r m . ,249, 305 (1911).
*
6-10, 1956.
BERNHARD WITKOP AND CALVrN M. FOLTZ
198
Vol. 79
sequence have not been formulated correctly. larger oxide rings in the course of the Hofmann degThis paper describes the preparation of the pure radation is a phenomenon frequently observed. epoxides, their catalytic reduction to the identical levorotatory benzylmethylcarbinol, their opening to the active’ phenylpropanediols and the assignment of stereochemical configurations to all of these transformation products and the mechanism of their formation (Chart I ) , The bimolecular elimination in onium ions4 normally proceeds by attack of a strong base on the most available hydrogen atom in /?-position to the electron-attracting group. L-Ephedrine (Ia) because of its strongly electron-attracting /?-phenyl group has an especially labile hydrogen on a benzyl OCH3 OCHB position and should easily undergo P-elimination x SI1 (pathway A) which mould lead via the trans-enol VI11 to propiophenone (IX). Only minor amounts of propiophenone are found when the quaternary methyl base of ephedrine is distilled with steam. I : > O zXI11 H2-x(cH2)2 The major product is an optically active /?-methylstyrene oxide (111). This indicates the preference for another pathway B.’ There elimination of triThe mechanism of the internal S N ~reaction ’ in methylamine occurs by an intramolecular dis- pathway B requires that no change of configuration placement reaction with Walden inversion, similar occurs a t the carbon C(1) carrying the displacing to the epoxide formation from halohydrins. hydroxyl group. The formation of the epoxide and elimination of trimethylamine leads to Walden inH H n. H version and trans ring-closure a t C(2). Ephedrine is ~~~-erythro-l-phenyl-l-hydroxy-2-methylaminopropane. C(1) has been correlated with D(-)mandelic acid.l* Written as in Chart I C(1) has the Lo-configuration. C(X), the R o ~ a n o v Icar~~ bon, has been correlated with L( +)-alanine13b and has an LS- or
[email protected] The epoxide from L-ephedrine (I) must therefore be a transI / CBHI-C-C-C€II epoxide (111), and, conversely, $-ephedrine, which cHO ~H5>c-c( I ‘ i I] differs from ephedrine only by the opposite DG03 NRa configuration a t C( 1),I5 as a threo-compound (11), VI11 yields a cis-epoxide IV in accordance with the general stereochemical rules established for internal displacement reactions.I6 C~H5-C-CH2-CH~ The trans- and cis-epoxides 111 and IV, which I/ 0 were freed of accompanying propiophenone by reIX action with Girard P reagent, like ephedrine and The synthesis of epoxides from quaternary de- +ephedrine, differ only in the configuration a t the rivatives of (phenyl)-ethanolamines is a M ell benzyl carbon. This was proved by catalytic reduction of the known reaction.6t6 A third type of cleavage is shown by the diastereoisomers of hydroxylaudano- two epoxides. Hydrogenolytic opening of the sine (X) which undergo reverse aldol cleavage to XI oxiran ringl7*l8occurred only a t the benzyl ether and XI1 prior to the formation of the normal linkage. The levorotatory liquid benzylmethylmethine XIII.7 The quina bases, as tertiary and carbinol obtained from both epoxides was converted quaternary bases, undergo elimination commonly to the crystalline 9-toluenesulfonate. Both toluby pathway A to form quinotoxines but the for(10) H. W, Bersch, Angcw. Chcm., 64, 59G (1952); H . Rapoport 76, 5329 (1953). mation of epoxides also has been observed.8 The and J. B. Lavigne, TEISJOURNAL, (11) N. R . Easton and V. B. Fish, i b i d . , 77, 2.547 (1955); J. Weinpreparation of narceine from narcotine metho- stock, J. Org. Chem., 21, 540 (19%). chlorideg follows pathway A. The formation of (12) K.Freudenberg, E. Schoffel and E. Braun, i b i d . , 64,234 (1932).
ZH8
4
cf
(3) L. Reti, Ephedra Bases, in “The Alkaloids,” by R . H. F. (13) (a) M. A. Rosanov. THISJ O U R N A L , 28, 114 (1906); (b) K. Manske and H . L. Holmes, Academic Press, Inc., New York, N. Y., Freudenberg and F. Nikolai, A n n . , 510, 223 (1934); W. Hiickel, Vol. 111, 1953, p. 339. Dcut. Apofh. Zlg., 96, 302 (1955); H. K. Mtiller, Ann., 598,70 (1956). (4) For a comprehensive review, cf. C. N. Ingold, “Structure and (14) Cf.K.Freudenberg, Monafsh.. 85, 537 (1954). Mechanism in Organic Chemistry,” Cornell University Press, Ithaca, (15) E. Schmidt, Arch. Pharm., 251, 320 (1913); 263, 52 (1915); N. Y., 1953, p. 420. H. Emde, Hclv. Chim. Acta, 12, 365 (1929). (16) Some leading references: (a) D. Y.Curtin and E. K. Meislich, (5) T. V. Braun and W. Teuffert, Bcr., 68, 2210 (1925); 66, 2178 (1923). THISJOURNAL, 74, 5905 (1952); (b) N. H. Cromwell, G. V. Hudson, (6) J. Read and I. G. h.1. Campbell, J . Chcm. SOL, 2377 (1930). R. A. Wankel and P. J. Vanderhorst, i b i d . , 76, 5387 (1953); (c) S. J. (7) R. Rohinson and S. Sugasawa. i b i d . , 789 (1932). Cristol and W. P. Norris, i b i d . , 76, 632 (1953). (8) Cf.P. Rabe, K. Dussel and R . Teske-Guttmann, A n n . , 661, 159 (17) Cf. P. Tiffeneau and E. Fourneau, Compt. rend., 146, 697 (1949). (1908). (Q) W. Roser, i b i d . , 247, 167 (1888); P. Rabe, B e y . 40, 3280 (18) W. F. Whitmore and A. I. Gebhart, T a r 8 JOURNAL, 64, 912 1907). (1942).
I 3CH3
m
I
ISL
ominopropane)
ominopropane)
retention a t C(I)
retention a t C(2)
retention at C(I)
,-/,
A
r-
P-I
\
f?)
Pd/C HZ
V
Y
7sH5
C6H5
PTD- e r y t h r o - I- Ph e ny I1,2-propanediol; dibenzoate m.p. 95.5-97O
[% -62.9'
C6H5
I
I I
H-C-OH (DG) inversion I at C(I)
Chart 1.-The
199
STEREOCHEMISTRY OF EPHEDRINE AND $-EPHEDRINE
Jan. 5, 1957
inversion
CHz
-
H0-C-H (LG)
I
rn -
L D-gw-i-Phenyl2-hydraxypropane, (-) - benz y I met h y Ic a r b i no1 ;
D - t h o - I P h e n y I-
p - t c l u en esulf on a t e, m. p. 72"
1,2-propanediol, m.p. 6 2 ' [ a l o - 6 O 0 dibenzoote, m.p. 89.5-91" re30 = o
i3lD-25.l=
Conversion of +Ephedrine and Ephedrine into D-glycero-1-Phenyl-2-hydroxypropane via the (+)-cis- and trans-b-Methylstyrene Oxides.
enesulfonates from 111 and IV had the same melting point (72') and rotation ([cr)D -25.1') as reported in the literature for D-glycero-l-phenyl-2hydroxypropane (V, Chart I).19,20 When lithium aluminum hydride was used for the reduction of the epoxides no readily crystallizing p-toluenesulfonate could be obtained. This indicates, as has been observed previously,21that S N ring ~ opening of unsymmetrical epoxides with metal hydrides leads t o mixtures of both possible alcohols. With the two pure epoxides I11 and IV available, the preparation of the pure glycols was attempted. The epoxides which are fairly unreactive toward sodium hydroxide and methoxideaJ2readily opened up in aqueous medium on addition of a catalytic The free glycols did amount of perchloric not crystallize, not even on prolonged standing.24 The reason for this behavior became evident on benzoylation: From the cis-epoxide IV the immediately crystallizing dibenzoate had m.p. 89.591', [o!]~~DfO', the mother liquors of this preparation yielded another dibenzoate, m.p. 95.5-97') [ a l Z o-62.9') ~ identical with the dibenzoate of the major product of the hydrolysis of the transepoxide 111. Acid-catalyzed opening of the epoxides, therefore, in the case of IV and possibly also (19) H. Phillips, J . Chcm. SOC.,123, 44 (1923). (20) S. Winstein, M. Brown, I(.C. Schreiber and A. H. Schlesinger, THISJOURNAL, 74, 1140 (1952). (21) A. Feldstein and C. A. VanderWerf, ibid.. 76, 1626 (1954). (22) J. Read and I. G. M. Campbell, J. Chcm. SOC.,2679 (1930); N a l u n , 125, It) (1930). (23) Cf. C. E. Wilson and H. J. Lucas, THISJOURNAL, 58, 2396 (1936). (24) A. McKenzie, E. M. Luis and A. G. Mitchell, Bcr., 66, 798 (1832).
in the case of 111, leads only to partial inversion a t C(1). In addition to the normal nucleophilic attack of HzO a t C(1) with inversion of configuration, there has to be considered quasi-unimolecular ring opening of the oxide-conjugate acid XIV and subsequent rapid reaction of the carbonium ion X V to give both glycols.25
IV &epoxide
XIV
H HO
OH
1
H
H O OH ~
+
CsHa-C-C-CHa I I
1
4
c6t)f-{-CHa
H
OH H
VI1 erythro-glycol
H
XV
XVI
VI threo-glycol
Epoxides, with two identical substituents such as optically active trans-2,3-epoxybutane or -stilbene oxide and meso-2,3-epoxybutane or -stilbene (25) R. G. Kadesch, TEISJOURNAL, 68, 41 (1946).
200
R E R N f I h R D \$'ITKOP
AND CALVIN
have been reported to give good yields of the pure glycols with no sign of crossover from weso to d,l. 22.23,26 This dual pathway of acid-catalyzed ring opening a pviori makes exact assignments of tizreo arid erythro configurations to the two glycols irnpossible. The following paper describes the synthesis of the pure racemic glycols and of the oxide of cis-0-methylstyrene by unambiguous methods. The synthetic experiments confirm the assignments represented in Chart I.
Experimental*' D-threo-l-Phenyl-l,2-epoxypropane (111)from I-Ephedrine (I).-A solution of 113.4 g. of hydrated, U.S.P., ephedrine alkaloid in 150 ml. of methanol was treated with 88.0 g. of methyl iodide in several portions. The mixture was left for an hour a t room temperature and then treated with a solution of sodium methoxide prepared from 14.3 g. of sodium and 400 ml. of methanol. The resulting mixture was treated with 88.0 g. of methyl iodide and allowed t o stand overnight. The crystalline methiodide, 143 g., was collected; i t softened a t 207" and was completely melted a t 214'. The salt was dissolved in 300 ml. of water and treated with silver oxide freshly prepared from 99.7 g. of silver nitrate. The mixture was allowed to stand overnight and then filtered. The washings and filtrate were combined and steam distilled. Four liters of distillate was collected. The distillate was saturated with sodium chloride and extracted with ether. The ethereal extracts were washed with hydrochloric acid, saturated sodium chloride solution, combined, dried and evaporated. The residue was 24.7 g. (29.7%) of a straw-colored liquid, [a]''D 36.9" (c 1.09 in chloroform). The presence of a ketonic contaminant in this residue was indicated by a small peak a t 5.93 p (pure liquid). A preliminary distillation of 2.89 g. of the crude epoxide through a short Vigreux column yielded 1.40 g. of a ~ (c colorless liquid, b.p. 85.0-86.0" (17 mm.), [ a l Z o47.2' 1.IO in chloroform); there was only very weak absorption a t 5.93 p . The careful fractional distillation of the remainder of the residue over a high-precision fractionation column resulted in extensive decomposition. After the following fractions had been collected: 1.51 g. of a colorless liquid (fraction I ) , b.p. 87.0-87.5' (15 rnm.), nZuD1.5190, [ a I z o D 48.2" (c 1.10 in chloroform), very weak infrared absorption at 5.86 and 5 . 9 ? ~ ~and ; 2.09 g. of a colorless liquid (fraction 111, b.p. 87.3 (1.5 mm.), 1 2 2 0 ~ 1.5202, [ c x ] * ~ D 50.0; (c 1.17 in chloroform), CYD 117.6" (pure liquid); the infrared spectrum showed the following major bands: 3.39m, 6.22w, 6.68m, 6.84m, 7.02123, 7.27m, 7.47w, 7.65w, 8 . 0 2 ~8.30w, ~ 8.74w, 9,83m, 9.81m, 10.50m, 11.64s, 12.24w, 13.06s, 13.48s and 14.35s. Both fractions I and 11 were used in subsequent experiments. D-erythro-l-Phenyl-l,2-epoxypropane(Iv) from d-#Ephedrine (II).-A solution of 53.8 g. of methyl-#-ephedrine methiodide in 27,5 ml. of water was treated with a slight excess of freshly prepared silver oxide. The mixture was allowed to stand overnight a t room temperature and then was filtered. The filter-cake was washed with a small amount of hot water, arid the filtrate and washing combined and steam distilled. Two liters of distillate were collected, saturated with sodium chloride and extracted with ether. The ethereal extracts were washed in the same way as described in the ephedrine degradation. The combined ethereal extracts were concentrated t o about 500 ml., dried and evaporated. The residue was 13.3 g. of a colorless oil. The presence of a ketonic contaminant in this residue was indicated by a peak of medium intensity a t 5.92 p in the infrared spectrum of the crude epoxide. Nearly complete removal of this contaminant was effected by treatment of
~~______
( 2 6 ) C j . D. lieulos, C o m p t . ? e n d . , 216, 771 (1943); 218, 795 (1944). A u u ; . ~ o r 14 : ~ PROOF. Retention of configuration in the acid-catalyzed ring opening of stilbene oxides recently has been reported: T. I
